# Top-rated ScreenCasts

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Residue Curve Modeling using Matlab/chap16/residue.m (8:00) (msu.edu)

Residue curves are powerful guides for distillation column design. Residue curves can be generated using bubble temperature calculations as described in the textbook. This screencast describes the strategy to generate a residue map by generating a series of curves and then inferring the location of the separatrices (distillation boundaries).

4. Selecting Stable Roots (1:11) (msu.edu)

Selecting stable roots is often one of the confusing aspects in working with cubic equations of state. This screencasts gives a visual picture of how the roots and stability are related to the vapor pressure and EOS humps at subcritical temperatures.

This sample calculation for methanol+benzene shows how to quickly generate the Tx binodal in Excel (uakron, 11min) using the Margules Acid-Base (MAB) model and the Excel iteration feature.(10min, uakron.edu) You generally need to start manually by setting the initial guess for the dilute component in each phase equal to the reciprocal of its infinite dilution activity coefficient. After a couple of iterations, you can set the "guess" cell equal to the "calculated" cell, and let Excel do the rest. Once you get one temperature right, you can usually just drag the fill handle to get the complete Tx diagram in short order. It is best to start at a low temperature to ensure that you detect LLE if it exists.

Note: This is a companion file in a series. You may wish to choose your own order for viewing them. For example, you should implement the first three videos before implementing this one. Also, you might like to see how to quickly visualize the Txy analog of the Pxy phase diagram. If you see a phase diagram like the ones in section 11.8, you might want to learn about LLE phase diagrams. The links on the software tutorial present a summary of the techniques to be implemented throughout Unit3 in a quick access format that is more compact than what is presented elsewhere. Some students may find it helpful to refer to this compact list when they find themselves "not being able to find the forest because of all the trees."

Comprehension Questions
1. Continue the temperature range to 380K with a feed composition of 60mol% methanol. What are the phase compositions and phase amounts in that case? (ANS. 0.299, 0.701, 75%beta-rich).
2. Continue the temperature range to 400K with a feed composition of 45mol% methanol. What are the phase compositions and phase amounts in that case?
3. Generate the binodal for methanol+nPentane for T=[400-460]. At 400K with a feed composition of 60mol% methanol, what are the phase compositions and phase amounts in that case?

Heat Removal from a Chemical Reactor (uakron, 8min) determines heat removal so that a chemical reactor is isothermal following the pathway of Figure 3.5b using the pathway of Figure 2.6c if a heat of vaporization is involved. The reaction is: N2 + 3H2 = 2NH3 at 350C and 1 bar. The pathway to go from products to the reference condition is to correct for any liquid formation at the conditions of the product stream then cool/heat the products to 25C (the reference temperature), then "unreact" them back to their elements of formation. Summing up the enthalpy changes over these steps gives the overall enthalpy of the reactor outlet stream. The same procedure applied to the reactor inlet gives the overall enthalpy of reactor inlet stream. Then the heat duty of the reactor is simply the difference between the two stream enthalpies.

Comprehension Questions:
1. Use this approach to compute the heat of reaction for 2 CH3OH = CH3OCH3 + H2O at 250C and 1 bar. Compare to your answer when using the pathway of Figure 3.5a.
2. Methanol is a liquid at 45C and 2bars. Compute the enthalpy of a stream that is 100 mol/h of pure methanol at 45 C and 2 bars according to the method of Figure 3.5b. Hint: this is different from the pathway of Figure 2.6c because it includes the heat of formation.

This screencast shows binary bubble, dew, and flash sample calculations (uakron, 19min) for methanol and ethanol. It complements the previous video by showing how the bubble and dew pressures relate to the Pxy diagram. It supplements the previous video with examples of numerical results for the bubble and dew temperatures. An isothermal flash calculation requires a different approach, but it also encompasses the bubble and dew temperature and pressure calculations. In a flash calculation, the bubble result is recovered when V/F = 0. The dew result is recovered when V/F=1.

Comprehension Questions (Assume the ideal solution SCVP model.):

1. Estimate the bubble pressure (mmHg) and vapor composition of methanol+ethanol at 50 C and xM = 0.4. (Note that the SCVP model should be used now.)
2. Estimate the dew temperature (C) and vapor composition of methanol+benzene at 50 C and yM = 0.4.
3. Estimate the vapor fraction and vapor/liquid compositions of methanol+benzene at 50 C, 355mmHg, and zM = 0.45.
4. Estimate the vapor fraction and vapor/liquid compositions of methanol+benzene at 50 C, 365mmHg, and zM = 0.45. (Hint: think carefully.)

Molecular Nature of Entropy (uakron.edu, 5min) Entropy is often related to chaos or disorder, but it has a specific, mathematical definition in thermodynamics. There is nothing metaphysical about it. This very brief presentation introduces the conceptual basis of how the arrangements of molecules between boxes can be related to the flow of work energy, or lack thereof, depending on how the process is conducted. This conceptual basis is expanded in Section 4.2 to permit quantitative calculations of entropy changes based on molecular configurations.

Hints for Generating LLE Envelopes (2:25) (msu.edu)

This screencasts makes several recommendations that help generate LLE phase envelopes most successfully.

This example shows how to predict activity coefficients in Excel using the Margules Acid-Base (MAB) model.(8min, uakron.edu) Sometimes you just need a quick estimate of whether to suspect an azeotrope or LLE or some other anomalous behavior. If the MAB model indicates a possible problem, it's time to go to the library or the lab and validate your model with experimental data.

Note: This is a companion file in a series. You may wish to choose your own order for viewing them. For example, you should implement the first three videos before implementing this one. Also, you might like to see how to quickly visualize the Txy analog of the Pxy phase diagram. If you see a phase diagram like the ones in section 11.8, you might want to learn about LLE phase diagrams. The links on the software tutorial present a summary of the techniques to be implemented throughout Unit3 in a quick access format that is more compact than what is presented elsewhere. Some students may find it helpful to refer to this compact list when they find themselves "not being able to find the forest because of all the trees."

Comprehension Questions
1. Order the following binary systems from most compatible to least compatible according to the MAB model:
(Note: negative deviations from Raoult's law indicate greater "compatibility," although they may generate azeotropes.)
(a) ethanol+water (b) ethanol+benzene (c) ethanol+diethylamine (d) n-pentane+n-pentanol (e) n-hexane+benzene
2. Pick a couple of binary systems from the Korean Database (Hint: use Internet Explorer for KDB) and compare the experimental data to the MAB predictions. Refine your predicted M1 parameter by calling the solver to minimize the sum of squared deviations between the predicted and experimental pressures. If there was an azeotrope in one of your systems, did the MAB model miss it or was it qualitatively correct?

10.04 - Multicomponent VLE & Raoult's Law Calculations Click here. 46.6667 3

This example hypothesizes a "pre-quel" to Example 10.1 in the form of a liquid reactor at 20 bars and asks what temperature the reactor must have been in order to result in the flash at 320K and 8 bars if no heat was added. This requires an adiabatic flash calculation. (7min, uakron.edu) The procedure demonstrated here applies the enthalpy pathway of Fig. 2.6c, with Eqn. 2.45 to estimate heats of vaporization. With this approach, you should be able to solve for mass and energy balances of any mixture at any vapor fraction. You should watch the video about Multicomponent VLE for Ideal Solutions before this one (see link above).

Note: This is a companion file in a series. You may wish to choose your own order for viewing them. For example, you should implement the first three videos before implementing this one. Also, you might like to see how to quickly visualize the Txy analog of the Pxy phase diagram. If you see a phase diagram like the ones in section 11.8, you might want to learn about LLE phase diagrams. The links on the software tutorial present a summary of the techniques to be implemented throughout Unit3 in a quick access format that is more compact than what is presented elsewhere. Some students may find it helpful to refer to this compact list when they find themselves "not being able to find the forest because of all the trees."

Comprehension Questions
1. Make a spreadsheet like the one in the video. Modify the compositions  to make a binary system like Example 10.2. Can you reproduce the results of Example 10.2?
2. Suppose a reactor was at 380K and 2MPa with a composition of {0.115, 0.335, 0.15, 0.15, 0.25} for {propane, isobutane, nbutane, isopentane, npentane}. What would be the adiabatic T&q of this stream exiting a valve at 8 bars?